We plan to define the fine structure and properties of the intra-luminal phases which occur during normal fat digestion both in in vitro and in vivo systems. Our preliminary observations suggest that a number of crystalline and liquid crystalline phases co-exist with a micellar liposomal phase from which the digestive products are presumably absorbed. We will continue our studies to define the physical-chemistry of bilirubin conjugates and related tetrapyroles and porphyrin-biliberdin protoporphyrin in aqueous and bile salt micellar systems. We will continue our work to understand the role of mucus glycoproteins secreted by the gallbladder wall in the formation, nucleation and growth of gallstones. Finally, we will continue our studies using quasielastic light scattering spectroscopy to define the structure, properties, kinetics, size, shape and composition of precipitating cholesterol-rich phases in model and native bile systems.